MEMORANDUM
To:Distribution
From:George R. Neil
Subject:FEL Upgrade Project Weekly Brief – October 29-November 2, 2007
Date:November 2, 2007
Highlights:
The Gun Test Stand HVPS is under pressure in preparation for its first HV test next week. The GTS diagnostic beamline has been prepared for its vacuum baking which will commence today. We delivered to our THz lab a 16 Tesla solenoid magnet to be used in materials studies (it will also be useful in discovering the effect of stray fields on the FEL linac operation 4 meters below!). We have also been doing a lot of preventative maintenance on the FEL hardware in preparation for bringing beam up again in late December.
Management:
We have been doing the final approval sign offs of the budget packages funded under the first increment of ONR funding which arrived last week.
We met to solidify our approval and test readiness procedures required for full operation of the Gun Test Stand. That appears on track and the required documentation and signoffs have been identified.
We have also been coordinating our running plans for the year with the rest of the lab. It appears that we will be able to operate throughout the year except for June and the first two weeks of July due to a shutdown for cryo refrigerator work.
Gwyn Williams met at LSU to discuss future light source development collaborations.
Injector:
The GTS beam line was prepared for vacuum bake during the week after the Vacuum Group installed a much needed Residual Gas Analyzer. The bake was started early today. The old IR Demo gun vacuum chamber that served as temporary chamber for the GTS gun electrodes was sealed off with blank-off flanges and transported to the machine shop. This chamber will be pumped down and bolted to the new SF6 tank for the pressure testing scheduled for next week. We held a GTS progress meeting on Tuesday where the Safety Systems Group reported that PLc's have been powered up this week as part of initial testing and system troubleshooting.
We started collaborating with Philippe Piot's group at NIU on injector modeling by sending him field maps of solenoids and cavities.
D. Bullard finished polishing the FEL gun electrodes which are ready for cleaning early next week. He also helped re-building the high pressure rinser used for cleaning the SRF cavities. This time the gun electrodes will undergo high pressure rinsing after the usual wet chemical cleaning. Most of the internal FEL gun parts are being wet cleaned for UHV conditions by the Vacuum Group in preparation for assembly next week.
The buncher cavity has been prepared for baking the injector beam line.
RF
RF Zones 3 & 4 were acid cleaned and flushed this week. The LCW flow improved for each zone from 32 & 35 gpm respectively to 65 gpm. Zone 2, the Buncher and the Quarter will be treated next week. The various vendors will be contacted to determine their equipment can withstand the acid cleaning. The Buncher cavity was prepared this week for a beam line bake to clean-up the vacuum after the SF6 Gun leak.
GTS HVPS
The SF6 system for the GTS is nearly finished. It is being cleaned of moisture and dust. The SOP to safe and operate the GTS HVPS will be started next week.
Instrumentation and Controls:
The major efforts continue to be the Gun Test Stand and completing the Lab 5 LPSS. At the beginning of this week we successfully managed to generate 100 ns pulses with resolutions better than 1 ns. These high precision signals were generated using a DG-535 which is a commercial pulse generator. The interface to this device was installed, checked out, and verified to work properly. These two signals are used to trigger the first Pockel Cell of the Drive Laser regenerative amplifier. After this was tested with the actual hardware and verified to work properly we discovered that we would in fact need to generate two more channels to trigger the second Pockel Cell. To better utilize the instruments that we have available we decided to remove the DG-535 used for triggering the WESCAM and replace that with a fixed delay Timer Card. This second DG-535 is now placed in the GTS control racks and once the software is ready to control this we will begin configuring the two channel outputs. The fixed delay Timer Card is currently being configured to generate the proper delay signals.The timing parameters have all been configured and tested. We are continuing with the configuration settings to trigger on both rising and falling edges. Once this is completed we will install this card to provide both the timing signals for the WESCAM as well as other camera synchronization.
The SF6 system is in its final shakedown. There were 2 very minor leaks that required finding a bigger wrench... The system is being dried out using the instrument air. SF6 gas will be filled next week to allow for HVPS testing. The SF6 panel meter was configured and tested successfully. The difficult menus of the OMEGA meter managed to make this a more complicated task than originally expected. Once the navigation between these menus became easier the settings were all configured to read the pressure transducer readback from 30 inHg to 15 psi. This was tested and verified to work properly.
Other work includes looking into the M55/56 chassis and preparing forthe FEL injector bake. There has also been progress on the LPSS master software.
Electron Beam Transport:
Improvements and Upgrades
Gun Test Stand (GTS)
•In building the SF6 Gun Tank system, the JLab Shop welded flanges and ground smooth the inside of the Outer Conductor Adaptor (the spool leading to the High Voltage Power Supply Tank).
•The test of the House Air Line to the SF6 system was completed on Tuesday morning and the line is commissioned.
•Matt Marchlik continues work on the hutch for the drive laser.
SF Sextupole Magnet Testing
•Magnet Test advanced to the third magnet on the test stand.
High Power Optics Risk Reduction
In last week’s report I wrote that the analyses required to extract absorptive loss from the thermographic data was complicated by conduction from the sample to the aluminum mirror holder. While I had a plan for an insulating holder, Joe Gubeli had a more elegant idea. He quickly drew it up and I received the part from our machine shop yesterday. I have just started preliminary testing, and find that I need to reposition the IR camera and make a couple of other changes to get good data. I’d also like to add the ability to irradiate the mode area with UV light to see how this influences the loss at the IR. To that end, I calculated the amount of power available from a high power Xe arc lamp, and it appears to be sufficient. I am setting up a test to see if I can image the source to a small enough area to be useful, and get the UV power required.
Optics
The optical transport is now seeing its lowest vacuum level of 1e-7 torr. The addition of those ion pumps last week not only brought the vacuum level down but, more importantly, it allows us to have a very quick pump down. If we have to in work in the transport we can have the system operational after repairs in a matter of days instead of the typical one week Given the difficulty in installing Turning Mirror Cassette (TMC) 1 it was decided to move to install TMC 4. The installation of TMC 1 would require the repositioning of mirrors cans 2 and 3. In addition the location of TMC 1 will change when the upgrade collimator is installed. TMC 4 (the first turning mirror assembly upstairs) should be able to “drop” in place without shifting the other mirror assemblies. We are preparing a quote to replace the mirrors in the transport with dielectrically mirrors centered at 1.6um. This should allow us to send a larger fraction of 1.6um light upstairs. The output coupler mirrors and frames that should have been sputtered and brazed this week have, unfortunately, been delayed again. The ion gun in the sputter chamber is sputtering some unknown metal on some test samples. Tests are underway to determine the metal species as well as the mechanism for this sputtering. Neither the optics nor the frames will get gold sputtered until this is rectified. We have received the mechanical drawing for the existing ‘collimator-lite’. We are designing a shield to prevent the first of the three optics in this vessel from absorbing stray light.
Lasers and Optical Diagnostics:
The measurement on the second harmonic pulses for the Antares laser shows over fifty percent conversion efficiency with individual pulse energy up to five hundred micro-Joule. We also measured the pulse duration which appears to be about fifty picoseconds. The characterization on the spatial phase was not complete due to the failure of a diagnostic instrument and will be done once it is fixed. Testing of the DLPC shows good improvement over last week. We are putting much more effort on the diagnostics needed for running the laser and injector. The laser for the cathode scanner has been received and we will start to set it up next week with other collimating optics near beamline. We are now making preparations for moving the whole laser system into the GTS site.
Terahertz:
This week, work continued on the magneto-optical experiments on the U4IR beamline at the NSLS. We unfortunately discovered some problems in the data. One issue is the lack of repeatability from the previous runs in August. That problem may be due to an adjustment made to the steering of the beam into the spectrometer. We were unaware that the steering had been changed to optimize the throughput in the mid IR shortly before our run began. It appears that we will still be able to use data collected in the current configuration, but the lack of repeatability may limit our ability to publish the data. In any case, we are continuing to take measurements and accomplish as much as possible. The other problem we have seen in the data is more troubling. We see a fairly significant variation in the spectrum at different locations on the sample. The cause of this is not yet clear, but we are investigating this now. Hopefully we can resolve this problem before our run ends this weekend.
Though both Michael Klopf and Gwyn Williams have been away on travel for most or all of this week, headway continued to prepare the 16T magnet for installation in Lab 3 and for the acceptance test scheduled the week of 11/12/2007. Neil Wilson and his group did a fantastic job of preparing the documentation and scheduling to get the magnet craned up to the 2nd floor of the FEL on Wednesday. They placed the magnet on a heavy duty dolly and it can now be moved into location when ready. Other preparations regarding ODH hazard analysis are continuing and we are on schedule for the acceptance testing.
Finally, as an addendum to the THz report from last week, we had a meeting at AES on 10/22/07with Alan Todd and Hans Bluem to review progress on the compact THz source, discuss debriefings from several SBIR proposals, and begin developing a testing plan for characterizing the output of the compact source.
Word version: FEL Upgrade Project Weekly Brief – October 29-November 2, 2007